The present invention relates to an image exposing apparatus to expose a light-sensitive material by using rays of light each being of a different color and being emitted from plural light emitting elements.
There has been an image exposing apparatus which is equipped, for each color to be recorded, with an arrayed light source composed of plural light emitting elements, and is capable of exposing a light-sensitive material (a print material or the like).
FIG. 23 is a schematic diagram showing how exposure is carried out by a conventional image exposing apparatus of the aforementioned type. In this case, there are provided arrayed light sources 1, 2 and 3 each having a width which is nearly the same as that of print material 11, so as to expose the print material 11. In the example shown here, each of arrayed light sources 1-3 is structured to form a pattern of zigzag arrangement of 20 elements.times.2 rows (40 elements in total).
In this case, each of arrayed light sources 1-3 emits light for each of R, G and B colors to be recorded. When each of arrayed light sources 1-3 is subjected to the driving which is delayed in terms of timing in accordance with the conveyance speed, while print material 11 is being conveyed in the direction as indicated by the arrow, the same position on the print material 11 is exposed to light of R, G and B.
Incidentally, it is preferable that there exists a light source with which emergent light in a line having the desired density shown in FIG. 24 can be obtained simultaneously. For example, when emergent light in a line having a density of 100 dots/line is needed, 100 elements are required for each of R, G and B, and a light source wherein 300 elements in total are arranged in a line is required to be made. Namely, the desired density for a light source for obtaining emergent light of 100 dots/line requires 300 dots/line.
However, it is difficult to arrange all elements on one line as stated above, because the size of a light emitting element is limited. As described above, therefore, it is arranged so as to carry out operations of exposure in succession by providing arrayed light sources for respective colors.
Since a light flux emitted from an arrayed light source is generally diffused, it is necessary to form an image of light from a light source on the surface of a print material or to cause a light source to be in close contact with the print material.
Because of the necessity of this close contact between them and of forming an image of light from the light source on a print material, when an image forming plane is kept apart from the light source, the brightness of an image is lowered. From the practical point of view, therefore, it has been necessary to carry out exposure by shifting positions for arrayed light sources 1-3, as shown in FIG. 23.
When carrying out position-shifted exposure for each color to be recorded, it is necessary to stagger the timing for the driving signal to be supplied to each of the arrayed light sources 1-3, in accordance with the conveyance speed. For this reason, there has been a problem that the structure of a driving circuit and timing control are made to be complicated.
Doubling results when speed variation is caused in a conveyance speed during the period from completion of exposure for a certain color to be recorded to the exposure for another color with regard to the same pixel. To prevent the doubling, therefore, it has been necessary to strictly control the conveyance speed for print material 11.
Since a slight movement of print material 11 in the direction perpendicular to the conveyance plane changes the size of an image of a pixel on the print material and thereby contributes to the occurrence of doubling, it is necessary to accurately maintain the position of the conveyance plane. Due to this, a mechanism to accurately maintain the conveyance plane is needed for each of the three light sources mentioned above, and is further needed to be within a range (range A in FIG. 25) to cover all light sources. Further, there has been needed a mechanism to suppress movement in the direction perpendicular to the conveyance direction in the conveyance plane during the period up to exposure for another color, with regard to the same pixel.
Namely, when arranging arrayed light sources 1-3 for colors to be recorded for conducting recording as shown in FIG. 25, its range A is broadened, and therefore, exposure that is free from doubling and color unevenness has been difficult.
Further, for correcting an exposure amount, it is necessary to provide light-receiving means at positions each corresponding to each recording head and in this case, three light-receiving means are needed, which has been a problem.
Even in each arrayed light source, it is necessary to stagger the timing for the driving signal in the conveyance direction for each row representing the same color, because of the zigzag arrangement of plural rows in each arrayed light source. In this case again, there has been a problem that the structure of a driving circuit and timing control are made to be complicated.